The present invention relates generally to outdoor, high voltage switches and more specifically to shielding means for high voltage disconnect switches.
High voltage tranmission line systems are necessarily provided with switching means for connecting or disconnecting the transmission lines from a load, or to a source of power. The switching means commonly takes the form of a power circuit breaker which is adapted to automatically break a circuit when a fault is sensed, and a disconnect switch connected in series between the circuit breaker and the line. Unlike a circuit breaker a disconnect switch, (as the term is used herein) is ordinarily not adapted to break a "live" circuit, wherein a substantial current must be interrupted. Ordinarily, interruption of high currents requires apparatus such as a power circuit breaker. However, in order to allow maintenance work on power transmission lines and apparatus, it is frequently necessary to isolate the apparatus after the current-carrying circuit has been interrupted. Hence the need for isolating switching means of the type described herein. Such switches are frequently located in enclosed areas such as power stations and substations, and often operated in groups. Due to the high electrostatic potentials involved, the switches are commonly large in size, and mounted on elaborate insulators. Further, the physical configuration of the working parts of the switch is extremely critical owing to the extremely high electrostatic fields in which they operate.
Disconnect switches commonly comprise a moveable blade or arm of considerable length controlled by linkage which may be operated manually, or by electric, pnuematic or hydraulic means. Ordinarily the elements of the switch are exposed, the moveable blade portion being pulled free of engagement with the stationary portion and swinging through a large arc to effect opening of the switch.
Due to the outdoor location of the disconnect switches, and to their necessarily exposed design, they are susceptible to jamming due to ice, freezing rain and the like. Considerable effort has been expended to design switching mechanisms which will shed ice readily. Effort have been made to provide the element with surfaces of polytetrafluoroethylene and similar substances to minimize the adhesion of ice. However, frequently the ice simply encases the elements and is mechanically secured to them despite the relatively low adhesion of ice to the surfaces.
Other efforts have been made to devise switches which would fracture a coating of ice as they separate, however, considerably increased force is still needed to separate the frozen elements. It will therefore be appreciated that it would be highly advantageous to provide means for preventing a buildup of ice upon the working elements of a high voltage disconnect switch.
It is therefore an object of the present invention to provide shielding means that does not unduly interfere with the electrostatic field about a high voltage disconnect switch, yet eliminates an ice buildup thereon.
Another object of the invention is to provide means for keeping accumulated ice from a high voltage disconnect switch without interfering with the operation thereof.
Yet another object is to provide means for preventing ice from accumulating upon working parts of a switch, and for shedding the accumulated ice in response to operation of the switch.